Use the Ranking function to rank rows in a column. The ranking will automatically be calculated to give the largest value a 1 and then moves in descending order from there. You can use this function as long as the number of rows in your group is less than 250. You have the ability to make the column display just the rank or the rank and the original column value.
To find this function locate the 3 dots next to the column name. Once you have clicked a tool bar will pop up. Locate and click the trophy icon with the name Ranking above it. Once you have clicked the ranking button you will have the option of what to show in the column (value, rank, both). Choose the mode and click done which will then rank the column. See video below for a demonstration.