let’s start from fundamentals; by default when BGP is establishing the adjacency with another neighbor, that relationship will be formed using the IP address of the outgoing/closet interface to your neighbor. However this design might cause issues in some design.
Take a look at this topology : R1 fa0/1-2=========== fa0/1-2 R2 , R1 is connected to R2 via two interfaces for redundancy. R1 will use one interface to form the neighborship, let’s say fa0/1 in this case. If Fa0/1 goes down for some reason, our BGP relationship will go down immediately then another session will start using the 2nd interface. On a production network, this will definitely introduce an outage while another neighborship is forming.
To overcome this outage in the future, we can create a Loopback interface on our local router, then use it as the source of our TCP session while establishing neighborship by using
neighbor x.x.x.x update-source Loopback x command.
Now I go back to your question:
R4(config-router)# neighbor 188.8.131.52 update-source loopback 0
Can you now try to answer the question? if not, let me know then @lagapides or @ReneMolenaar might explain better