Transaction not confirming due to high mempool traffic

I’m involved in a trade (the maker is the buyer) in which the seller deposit transaction is not confirmed at the blockchain for more than one day because the fee is too low (the fees increased a lot suddenly). There is any easy way to solve it?

You could try a Child Pays For parent (CPFP), but it’s expensive and needs some technical knowledge, so it’s best to keep waiting if the deposit transaction is confirmed. Keep paying attention to blockchain explorers as Bisq might fail sometimes to recognize the deposit tx as confirmed.
If you see that it’s confirmed but it doesn’t appear as it at Bisq, do SPV resync.

If the seller deposit can’t get to the blockchain, what happens?
Can the seller make a new deposit wit better fee?
How long do you think we have to wait until the deposit transaction is deleted from the mempool?

CPFP can be made by any of you as there’s unconfirmed UTXO’s from buyer and seller waiting to be confirmed at the deposit transaction. Still, I don’t recommend as it’s complicated and most of the transactions get included sooner or later.
All mempools have their own rules on what tx keep or forget. From my experience, after 3 days some mempools can start to remove them.

Fees aren’t that high now, are you sure that the tx has not beeen confirmed? Go to Keybase so you can share personal details like deposit tx txid.