You have to tell the sender to pump the fee.

If he is not answering you, you can use child-pay-for-parent to pump the fee on wallets like Electrum or Bluewallet. If you use child-pay-for-parent to pump the fee, use 26 sat/vbyte.

By using child-pay-for-parent, you will send part or all the unconfirmed transaction to another address on your wallet. Before a miner can include your transaction (child transaction ) into a block, the miner has to include the parent transaction (this unconfirmed transaction) into a block as well, but the fee you paid for your transaction which is enough to get two transactions confirmed will make a miner to include both transaction into the same block early.