The straight-forward way is to fill the ADABAS buffers (Record buffer, Value Buffer etc. and Control Block) and then issue Direct ADABAS commands (L1, S4 etc.). This process is well documented, with great examples in SAG's documents.
There are vendors products to access ADABAS from within COBOL. Among them is the famous ADASQL.
For one client, my company developed Common Access Routines (AKA "black box") to get services from ADABAS to COBOL.