invinoveritaserum if you can afford to put your head above the parapet, here's what I would do:
During the session, ask how their recommendations on how to treat people who identify as trans fits into your work's established safeguarding procedures.
I know someone who did this when they got public sector training on trans awareness. They couldn't answer and this person then made a complaint to their boss about the training being completely inadequate and unlawful as it violated both the law as per the EqA and conflicted with existing safeguarding procedures. The bosses agreed and did not invite the training company back for the scheduled second session.
If you have time, I would go prepared by reading the Fair Play for Women website and WPUK and others on why mixed-sex facilities don't work for women and then prepare a few questions, along the lines of why do we have to respect the feelings of males who identify as trans as trans and insist on using our facilities, but not the feelings of females who wish a space free from male violence and the male gaze.
I'd also take a printout of the letter from the lawyers on the EqA showing that we have a legally protected right to female only prpvisions and the judgement in the Asher's cake case showing that we cannot be compelled to manifest a belief we don't have (or punished if we don't).
I would also ask the trainer if they believe that females - in language and in law - have the right to define themselves in a category of their own, separately from males.
With our own sovereign spaces, our own sports, the right to organise and assemble as females, again separately from males, to address inequalities, oppression and discrimination we face as females in a male-dominated world.
Because we currently have these rights as granted in the EqA and if their training conflicts with that, your employer is paying an external company on training you not only in how to break the law, but also expecting you to submit to having your own rights as a female violated. Without protest.
You might ask about liability insurance. Specifically, if the training company delivers the usual unlawful claims about how males who identify as trans as trans have a right to use female only facilities, you could ask how your employer can get around the conditions of liability insurance that the insured must adhere to the law or else the insurance is invalidated.
You might also ask, when a female has other protected characteristics, such as disabilities, race or religion in addition to sex, how these are accounted for in their training.
Usually, they completely ignore these by presenting everything in a way that implies that gender reassignment trumps them all.
If you are not in a position where you can speak out during the training, I would definitely record it for myself as a memory aid, then go through it afterwards point by point and write a critical review showing where their training/advice/claims conflict with the law, science, empirical data etc.
Depending again on what is safe for you, I would then send my review (anonymously if necessary) to the relevant people at my work and/or women's orgs and/or the media.
But what I think you might be able to safely do in any case, is to send an open letter at work thanking them prettily for the opportunity to learn more about people protected under the gender reassignment section of the Equality Act and ask when they will organise awareness training sessions on the other protected characteristics, because you feel that you could all learn so much from understanding the needs and feelings of other disadvantaged groups. Or something like that.