Hi Juan,
There doesn't seem to be much out there in the way of guides to replacing the speaker mesh; apparently one of the things in the way is the plastic frame that holds the earpiece speaker and sensor array. Since those assemblies are very similar in the iPhone X, there is an answer to that same question for that phone that describes the procedure.
[post|571366|iPhone X Earpiece Speaker Mesh Replacement - iPhone X - iFixit|new_window=true]
Since you've already replaced the speaker itself, you know how to take out that front assembly, so I won't bore you with the details; just remove the Earpiece Speaker and Front Sensor Assembly, then follow the instructions given in the answer above and you should be all set. Although the mesh is available many places, you can support iFixit and their repair advocacy by buying from them if you're so inclined.
[product|IF426-016|iPhone 11 Earpiece Speaker Mesh - iFixit Store|new_window=true]