Don’t bother, V1 is not longer supported and no longer works properly (even tough you can restore purchases properly, the newly made purchases are not beeing confirmed and google automatically refunds them after about 10 minutes, not to mention that the game will start crashing A LOT if you use the old version). We must wait for some update to patch StoreV2. Until then, 4.24 still works.
If you still want to disable store V2 and use V1, drop this in your config file:
[OnlineSubsystemGooglePlay.Store]
bUseStoreV2=False