Put your seed phrase in to Electrum, select BIP39 wallet, and select "Detect Existing Accounts", as I described above. If it can't find your segwit account, then you are going to have to start trawling through derivation paths in order to try to find it. Try incrementing the last number in the derivation path in the first instance, so for example:

m/84'/0'/0'
m/84'/0'/1'
m/84'/0'/2'
And so on.

Once you've actually found your coins, you should make a brand new Electrum wallet, have Electrum generate a seed phrase for you, write it down on paper, and then send all your coins to this new Electrum wallet, since otherwise they are still under a seed phrase created by a web wallet and therefore not in your sole custody.