To mesh, over wireless you would need (1) a Dual Radio AP - Which you already have (2) A power injector or power cord (3) A switch to plug APs in initially.
Configure the first IAP. Plug in a second, new IAP on the same physical LAN and allow it to get the configuration from the first and broadcast.
The next time you bring that second IAP up using just power, it should find the first IAP wireless access point without modification and just mesh.
Please see the kb article here: When does an IAP act as mesh portal or mesh point? https://kb.arubanetworks.com/app/answers/detail/a_id/1305