A more thorough explanation:

IPSE

Ipse means "the same" or "the very person". It comes from the Latin word "ipse" which means "he himself".

When John said "I will do it myself", he meant that he will do it ipse.

She wanted to talk to the ipse doctor who had treated her before.

The examples show how the word "ipse" is used to refer to the same person or thing. In the first example, John wants to do something without any help from others, so he will do it himself, or ipse. In the second example, the woman wants to talk to the same doctor who had treated her before, so she asks for the ipse doctor.