Appraisal disagreement advice

[Gav Sak]

I'm currently refinancing my live in home to have some cash on hand for another investment. I currently have a VA loan and doing my refi on a VA loan as well. An appraiser (that was appointed by VA loans) gave my home a really low appraisal value. In 2018 I refi'd and my home appraisal was 920k. My appraisal that came in yesterday was for 830k. Since the time between the 2018 appraisal and this appraisal I have done $40k+ in renovations. I live in hawaii and the home prices here have skyrocketed within the last year not to mention the last 3 years. Any advice on what I should do or on how should go about challenging this appraisal?