Use a non-SLP wallet, find the coins that correspond to the tokens you wish to burn, send those coins to yourself (or anyone). This burns the tokens.
What do you mean by find the coins?
Electron has a Burn tool as well (but didn't work for me until v3.5.1)
Ie., in the "Coins" tab in Electron Cash, find the "outpoint" that corresponds to the Tokens you were send (TX ID).
