Unlike importing, sweeping is basically sending the funds from the address associated with the private key to one of your Trezor/Electrum addresses. In other words, If you sweep, the private key will no longer contain funds.
Trezor doesn't allow sweeping private keys directly. You can, however, achieve that by using
Trezor with Electrum. If you already transferred the funds to Trezor (which is what I understood you did), there is no need to do anything else.