Dear Naqshe Zuhra ,

First, yes, higher stomatal density increase the photosynthetic rate by increasing stomatal conductance and CO2 assimilation rate.

Secondly, stomatal density can be modulated by overexpressing STOMAGEN/EPFL9 or silencing EPIDERMAL PATTERNING FACTOR 1, a positive and negative regulator of stomatal development respectively.

Article Enhancement of leaf photosynthetic capacity through increase...

https://www.frontiersin.org/articles/10.3389/fpls.2020.589603/full

Mind that these papers studied C3 plants. C4 and CAM plants are likely to be similarly affected, but I didn't read papers about them.

Stomatal parts are the ones through where the photosynthesis gas for exchange passes, and defintely if the density of the stomata bodies/pores increase per given area of leaf, then there will be an increase on photosynthesis.

Yes the stomatal density increases photosynthesis rate due to high carbon dioxide assimilation. Please go through the following paper:

Article Higher Stomatal Density Improves Photosynthetic Induction an...