need help asap thanks

hey all im on day 32 of my grow right now and its the most basic shit ever (cardboard box, tin foil, 2 60w led lights, bagseed). i noticed some flies flying around in my box a while ago and i just thought they were some fruit flies. i woke up this morning and i realized it was some fungus gnats because the fuckers ruining one of my plants already. its already noticeable the damage as seen in the pictures. what could i do to get rid of em? imma try the yellow sticky tapes and hydrogen peroxide because its the cheapest probably but im wondering if its safe for my plants at this stage. i began using 5-1-1 alaska fish fert nutes 2-3 days ago and its on its first feed right now. its in miracle-gro soil. besides this, at least in my opinion, plants are looking healthy.

also was wondering if it was possible to sex at this time from pictures lmk if anything catches ur eye! thanks!

fungus gnat damage pic 3

picss:

 

ive been reading they damage the plant tho doesn't damage = more low quality/less yield