how to processing images from different days

Dear group

I need to make a biome classification of a big area, for it, I put together four images from different days that cover my interest area (I already did using SNAP–> mosaicing)( all images are L2A). One of my images is from a different day than the others and show different brightness/color that the others ( I don’t know how to explain it, but look different), so I think I need to make a correction of it, maybe an angle correction or reflectance correction?
Could someone tell me what kind of analysis or corrections should I do when I concatenate images from different days? and what programs should I use for this?

Thanks so much