How to use Google’s Alpha-fold to predict the structure of a two-protein complex?
Are you asking how to take code developed to find the MFE (minimum free energy) structure of a single protein, and modify it to instead determine the structure of a two-protein complex?
Or are you asking if you can use this code, as is, to fold a concatenated combination of the two proteins, and in turn use this result as a surrogate for the predicted structure of the two-protein complex?
If you're asking the former, I would recommend contacting one of the code developers to ask them for guidance.  It's possible that they have already developed a prototype option to address this.
If you're asking the latter, that approach is problematic, for two reasons:

Folding the concatenated protein would constrain the last amino acid in the first protein to be next to the first amino acid in the second protein.  That's not a constraint that would make sense a priori for a two-protein complex.

You have to ask yourself if, in forming the two-protein complex, you envision both proteins unfolding and then refolding to do a global energy minimization— since that's what folding the concatenated protein would give you (with the additional constraint mentioned in point #1, above).  If, on the other hand, you would like the proteins to each fold into their respective MFE structures, and then (while essentially retaining those structures) find the MFE configuration for the two-protein complex, then folding the concatenated protein clearly would not give you that.