Look at the documentation under "tgcd" or in your console:

library(tgcd)

?tgcd

There is an example at the end of the entry. Instead of using "Refglow" you can use your own TL_data_set.

The minimal input for this function is then:

tgcd(your_TL_data, npeak = 3)

Or whatever your number of peaks are. Then you have to select your peaks with your mouse.

Best wishes,

Johannes