How to pool fractions after chromatography?
If all fractions contain the same protein, I'd combined all and concentrated the combined solutions to desired concentration using biochemical techniques such as dialysis. If they contained more than one protein, then I'd combined all fraction collected under the correct peak. However, it is better ask your supervisor (or adviser) before you combined them. The person who wrote the protocol knows which one to collect. Yet, you can look at following reference to get an idea how to concentrate the combined protein solutions:

Sarah M. Andrew, Julie A. Titus, Louis Zumstein, "Dialysis and Concentration of Protein Solutions," Current Protocols in Immunology 1997, 21(1), A.3H.1-A.3H.5 (https://doi.org/10.1002/0471142735.ima03hs21).