Because you say that it is on an IP Office system, and it is Basic setup not Essential, it isn't really easy or user friendly.

Start here:
https://marketingtools.avaya.com/knowledgebase/

Press the Blue box for User Guides
If the left hand drop down box, select Basic Edition
Now select 1400 from the tree at the left, then select Button Programming from the tree in the middle, and then Programming a Button and Button Functions under that.

or https://marketingtools.avaya.com/kn...ojects/manuals/Quick_1400_User_Guide.pdf for the pdf manual, page 56 is where button programming starts