ok it seems like a simple problem, but i am having problem I have a timer for each data set which resets improperly and as a result my timing gets mixed. Any ideas to correct it? without losing any data. Example

timer col ideally should be

timer , mine reads
1 3
2 4
3 5
4 6
5 1
6 2

how do i change the colum 2 or make a new colum which reads like colum 1 without changing the order of ther rows which have data this is just a example as my file lengths are 86000 long , also i have missing timers which i do not want to miss , this imples no data for that period of time.

thanks

EDIT: I do not want to change the other columns. The coulm 1 is the gps counter and so it does not sync with the comp timer due to some other issues. I just want to change the row one such that it goes from high to low without effecting other rows. also take care of missing pts ( if i did not care for missing pts simple n=1: max would work.