Someone may reply with better advice, but here's what I've got:
A. The easiest way (which you should not do):
1. 'Find Game Object' (by name and optionally by tag also). Store as 'ObjectToActivate'
2. Activate 'ObjectToActivate'
You should not use 'Find Game Object', because it is not efficient. It will search the entire scene until it finds the object, which can hurt performance
B. The better way:
1. Add ArrayMaker to your project
2. Store the object(s) to be activated in the array
3. 'Array List Contains' by name and optionally by tag also). If True, Store as 'ObjectToActivate'.
4. 'Activate 'ObjectToActivate'