For my part, if it's a small column, I would just throw out the resin and make a new column for the next run. For a large column, that would get expensive.

If the column does not need to be cleaned, just prepared for the next run, just run 2-3 column volumes of elution buffer through it until the small molecules have eluted.

This is excerpted from the Sephadex manual from Cytiva.

Cleaning

1. Wash with two column volumes of 0.2 M NaOH or a solution of a nonionic detergent. Washing the more porous Sephadex types (G-50 – G-200) with NaOH should be done outside the column because the gel will swell.

2. Reequilibrate the gel with 2–3 column volumes of buffer before your next experiment. When necessary, the gel can be removed from the column and sterilized by autoclaving at 120 °C, pH 7.

Thank you so much for your help. Have a nice day.