There are a few different ways of getting data into Adobe Target (see here), there are probably 2 options relevant in your scenario:
i) Pass the same data you send to GA as events/dimensions into Target as parameters, and then create the audience in Target
ii) If it's an audience of known users (i.e., identified via some sort of customer ID) then you could either use Customer Attributes or the Profile Update API (see here)
Note: I have seen customers use Customer Attributes, but based on the Experience Cloud ID cookie, in order to broaden this to audiences of unknown users; however, the challenge here of course is that these cookies will expire so the % of the audience that can be targeted will be lower, depending also on how frequently visitors visit the website