Looking on the internet deeply has found these results:

Let it to be done is the most popular phrase on the web.

Let it be done 11,490,000 results on the web	Let it to be done 1131,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
As it is written, so let it be done. So let it be written, so let it be done.	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

Let it be done

11,490,000 results on the web

Let it to be done

1131,000,000 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.