It sounds like this person isn't remembering the procedures then, even when you've explained it to them and they've already done the task before (Or they're just a lazy fuck that doesn't care one way or the other and maybe never will). There is no "fixing" the individual, you need to correct their behavior while also giving them plenty of opportunity to get it right and with all the tools and guides they need readily available. How long have they been working in that position? Maybe they just need more time.

As others have stated, if the directions aren't already in writing, you should either write them down for the employee or, better yet, make the employee write them down, then review it for accuracy. This should in theory help them commit the process to memory, plus now they have their own guide to refer to.

Another bonus (for you, not the employee) of getting the process in writing is that if/when this person messes up again, now you have something to point back to and say "Remember when we went over this and you wrote it down and I verified that your notes were correct? Did you follow those notes this time? If yes, why did (mess up) happen anyway? If no, why didn't you follow the notes?" Make this person explain themselves, don't just sit there and be mad and say nothing to them.

This could also be a case of weaponized incompetence/ learned helplessness. If they fuck up a lot, you stop giving them work, but they're still there getting paid anyway, right? Now you're just paying them to either stand around or do menial tasks and not what you actually hired them for.

Start documenting their fuck ups, and tell them you're doing so. You're better off having a paper trail to point to when you have to fire them.

It may be that your comms skills are good enough for most people but not for this person. One option you have is to improve them even further so that it goes beyond being sufficient for the normal people, and also becomes sufficient for this person.

For example, I have never had my instructions misinterpreted. I am autistic. In my experience, both autistics and neurotypicals tend to interpret my instructions with zero difficulty.

I am saying this to indicate that it is possible to use language in a way that works even for the people who need extra precision.

In the scenario you described, the use of the word “this” in the “send this to them” instruction was a predictable failure point in the communication.

Eliminating that word from that communication would have prevented this issue.

If you want to change the individual, have them do significant working memory training. If you want to solve the problem, consider establishing and enforcing a higher level of disambiguity in office communications.