Obviously usual caveat of all dogs being different etc applying...
But hopefully the meet up is planned on neutral ground outdoors/walk where dog can destress or be distracted by current owners?
I always found that, as much as needed, largely ignoring dog initially (no direct approaches, no voice stimulation etc unless they initiate) and letting them just be around us, sniff us where needed, soft positive voice if they are calm and seem interested/initiating, but basically putting zero pressure on dog for anything... treats sometimes helped if food- motivated dog too but again only if dog showing interest in me already... if not and they just wanted to walk away or spend their time metres away from me thats fine, they will still get used to your presence and voice from a distance even if it takes multiple "meets" like that before they choose to approach..
Its so hard as persons natural urge is to initiate contact, reassure, engage... whereas all the dogs natural urges may be to run/growl/cower etc...
Sorry if none of that is helpful 😅😅
My last hugely reactive foster dog only took 24hrs to come round and after full day and night of me leaving him to his own devices, he woke up and just decided I was his new human... but others take weeks to do that and even then can struggle so patience i guess ❤️❤️❤️