Hi @Anonymous,
Please modify you formula as below:
replace(variables('Testcomments'),'''','') // Replace the single quote with nothing


Further, if you want to leave space for the place where you put the single quote, you should use ' ', there should be a space between the single quotes:
replace(variables('Testcomments'),'''',' ')//Replace the single quotes with a space
And if you want a space to replace instead, you could get as below:

Use the above formula according to your real needs