since Electrum was mentioned above, i have to say there is no option to import a single multi-signature (private keys and redeem script) into Electrum. your only option is if the address was derived from master keys and you import those in Electrum.
if your address starting with 3 was a multi sig then your only option is to use the core wallet.
if your address starting with 3 was a multi sig then your only option is to use the core wallet.
Hi how to u use the core address my btc starts with 3