May 2019
Hey @pranasas1985
I suppose you've already accessed Armoury on the Tempest or any other station that lets you modify weapons, right?
It's been a while since I play ME Andromeda on PS4, but if I remember correctly you should be able to highlight the weapon you want to modify, then press Square to select one of the available modification spots. Press X to show list of mods that you use use for that spot and choose one. Voilà!
/Ataashi
May 2019