Where do I find this txid?
Double-click on your transaction in the "History" tab and you should see it in a new window. There is no need to provide us your transaction id. Once you double-click on your transaction, you should see "Replace by fee". If it says "True" then you can follow the instructions from my first post.
This is the fee I paid for the transaction. 0.0007164 BTC ( 31.4 sat/byte )
Yes, I can replace my fee.
When I change the value, Electrum gives me a new one, like 41.1 sat/byte. I just confirm but nothing happens. Do I need to change the option to Mempool, Estimated Time (which is set as default) or Static?