Yes. But. It all depends on your child and your local grammar system.
Is your local area opt-in or opt-out? Ie does everyone do the 11+ automatically? Or do you have to apply to do it for the schools you are interested in?
If it’s the former then your child maybe only needs to be in the top half of their class. If it’s the latter, they’ll need to be the top of their class.
So you need to check what standard of attainment applies in your area. You need to then compare this wit your child’s academic attainment so far and take a view on how much work is required.
Then to your child. Are they motivated (or likely to become motivated) to work for the test? You can only do the 11+ if they are on board.
Do you have a good working relationship? Will they let you tutor them? How do you have to accommodate their learning style or differences?
What type of tests are done in your area? How does your child rate in each area?
Eg DS finds maths and VR easy but comprehension & writing tricky. He’s already well ahead in the first 2 so we’ll do very little on those other than exam/format practice and speed training. We’ll do background learning in vocabulary and story building all the next 12 months to build his confidence very very slowly as otherwise he’ll refuse if we go too quick.
You’ll have completely different requirements based in your area and child, but DIY is totally do-able