Ensure twitter_api addon is activated in Zap site.

Download/Install AndStatus from F-Droid

Open AndStatus
Settings (Gear Icon) > Accounts > Manage Social Networks > Add (circle plus)
Type of Social Network: GnuSocial
Host: your Zap site (e.g. zap.dog)
Name of Social Network: name of your Zap site (e.g. Zap)

Go back to start.

Get Started
Type of Social Network: GnuSocial
Select network added in first part (e.g. Zap)
Username: Enter the channel nickname. (example: if pancho@somezap.site, just enter pancho)
Your social network password: your password
Add this account