It’s figuring out the counter play.

I play a lot of deck building card games and we generally figure out how to ‘tech’ against a dominant strategy. For example, is a deck someone has has a particular card or combo that wins unless you have card that beat it - you might include cards or build a deck that can and find yourself ‘teching’ against it. It sort of refers to a higher level of ‘technology’ when it comes to building that can counter the ‘meta’

To make the easier translation to Smash - if a strategy become dominant - you can add things to the way you play to ‘tech’ against it. Again, in this situation - it’s a Referance to the meta game, If an OP fighter stars seeing a lot of play and a certain move for them starts seeing a lot of play, other players might ‘tech’ against this ‘meta’ by figuring out what can beat it.