It is possible, yes. You are certainly the expert on the material. At the stage of publishing when it’s time for indexing to be done, you might be tired of it and ready not to look at it for a while, though! There are other tasks that will require your attention now, such as proofreading and marketing (which should be ongoing.)
If you are one of a team of authors, indexing will become more complicated as you juggle decisions.
Indexing is most efficiently done with dedicated indexing software, an investment in cost and time to learn. Again, not the best use of your time. That’s just the mechanical aspects – – the practice of indexing, the decisions to be made in term choice and arrangement, and the conventions, is a whole other field of study.
But let’s go back to the first point — that you are undeniably the expert on your topic. The indexer is the stand-in for your future reader, and our mission is to stand in the reader’s stead, thinking, “Where would I look for this subject,” and “under what term?” “Are there any alternate terms to be considered?” All the while adhering to the conventions of indexing and the particular publisher for your book.
You should have the opportunity pre- and post-indexing for input as well, so you won’t be sending your book off with one chance to get it right. You can send notes ahead of time, and if the schedule is not overly tight, there should be a day or two for review at the end. As well, I’ve queried authors during an index as to their preferences for certain entries.