Is this a correct grammar I the undersigned hereby authorize Ms Lim to do encashment of my SSS check?

The grammar is mostly correct, but there are a few improvements you can make for clarity and formality:

Revised Sentence:

"I, the undersigned, hereby authorize Ms. Lim to encash my SSS check."

Here's why the revision is better:

* "I, the undersigned": This is a more formal and clearer way to state that you are the person authorizing the action.

* Ms. Lim: Using "Ms." is a respectful title.

* Encash: While "encash" is technically correct, you can use "cash" for a more straightforward and common phrasing.

Final version:

"I, the undersigned, hereby authorize Ms. Lim to cash my SSS check."