Thursday's (Aug 18th) rail strikes! Can anyone help me understand how to change my ticket?

[Learningtosayno]

I was due to travel Newcastle - Manchester on this day (Thurs, Aug 18th). My trains has been cancelled.

My cancellation e-mail says:

Your ticket is valid for the next available TransPennine Express service that's departing from Newcastle, provided you're still within any relevant Operator and time conditions of your ticket (e.g. Off-Peak or Super Off-Peak). Go to "My Bookings" to find out the conditions of your ticket. You can visit our Off-Peak page to find out how to check which trains are Peak and Off-Peak.

(From Trainline)

However, the next two trains are both sold out? Will we be allowed on with the tickets we have? Or not because the train is full?

Thanks! I tried calling the station, but nobody is answering :(

You'll be allowed on but not guaranteed a seat

Yes, I understand that, and that's fine about the seat

I just really wanted to know if I was allowed on