Best way to fix mesh?

If its a small tear Ive just used a needle and thread

depending on the magnitude of the dmg, you might go to Joann's fabrics and find the lighter of their iron-on repair fabric.

set your iron near / just under 300°F. let it stabilize at that temp for a bit.
that should , and we mean "should" be enough heat to both melt the adhesive, and not destroy your netting.

there is about a 30° window to play with. 300 is the low'ish end of things.

also :
they sold, and i suspect still do, stick on t-rest repair kits. these stick pretty darn good, and work even better if you iron them on.
i patched my pack with them.

a decent thermometer is sop for using heat on such tasks.

cheers,
v.

Be sure to protect the neting around the repair tape with cloth strips so you iron doesn't touch the netting. Just sayin'…