How to best pre-process this image so the faint cell border is the most visible?

Question

I have tried using ImageJ/Fiji but I am not sure how to best de-noise the image. I tried using the denoise function in Fiji to no avail. I was wondering if I could get some guidance. I was informed I could use python algorithms but I am not sure what are the best ones either. Gimp is also an option but plugins are a little difficult to install on Mac.