Only choosing lower gas price is the way to lower the transaction fee. I use MEW Android app and choose low gas fee when I made an ERC20 transaction. You can try it.
Of course this is an option but the problem is when the Gwei is always irregular which makes this a little risky and can fail.
but with the right timing I think this could happen maybe it will take a little longer than usual in the transaction process but this will be much more profitable.
but remember this is risky even if you want I can suggest this is done at night because it is always effective at night because at certain times at night sometimes gwei will experience a hefty drop and I've tried it several times and it works