Account determination for non stock purchase order

When we pursuing the SAP tutorial of "Creating Purchase Order of Services" successful 1LE scope point for S4HANA unreality nationalist edition, it shows that the g/l relationship 51600000 is derived by worldly radical YBMM01. 

We would similar to alteration the predefined g/l account, but we cannot find the comparative relationship determination configuration successful IMG. Please counsel wherever tin we acceptable this relationship assignment?