If it's a 3 of 3 multisig, in order to import it into Electrum, you'd need all three xprivs (master private keys)
Go to file->New/Restore
Enter a name for your wallet
Select "multisig wallet"
Choose the multisig scheme (eg 2 of 2, 2 of 3, 3 of 3,)
Select "use a master key) if you have the xprivs or "use an existing seed" if you have the seed phrases
Enter the first xpriv, click next
Save the xpub , click next
enter the xpriv or seed of second cosigner, click next
repeat the procedure for the last cosigner
enter a password for the wallet for security, click next
And your multisig is restored.