The valuation from an appraisal should be a range that ideally comes in 5%-10% of what you were expecting. If they come in wildly out of range you should have your lender submit a reconsideration. Ideally they are working with the AMC to get the verbiage right and see what was wrong with the original comps. Appraisals are also subjective so understand where the appraiser is coming from.
If the reconsideration doesn’t prove fruitful a new appraisal is always an option.
Unless you have a bad lender it’s really outside of their hands they should assist, but if they do everything for you then it’s not their doing.
I have done both of these above and would be happy to chat more about what I submit up if your lender isn’t doing it.
I would to the maximum extent practicable do the most so you know you're maximizing the value of your property. Provide detailed SOW/Budget, comps from the MLS and why you picked them, and optimizing the rehab budget to keep cash in low.
Hope this helps!