Send them some BTC (to their storage address) that’s enough for them to use both the incoming tx from Relai and the tx you send in a new transaction to themselves, with a fee high enough to get the (I assume) low fee Relai transaction confirmed.

It's not mine. It's my noob friend trying to send BTC from Relai into cold storage.

you can do a CPFP from your side to bump it, if you are the destination of the payment.
Use Electrum or Sparrow and just click on that pending tx and bump the fee with an UTXO from your wallet.

Read more about CPFP here
https://bitcoinops.org/en/topics/cpfp/

DarthCoin

bitcoin

Boost/Accelerate TX Services

It's not mine. 

https://stacker.news/items/437966

Its for a noob friend on the other side of the planet.

I might have to get him on a call. This is probably the cheapest option.