Without specifics we are going to have to make sum assumptions...first assumption the molar tooth is erupted and the supernumerary tooth is impacted under the erupted molar. If this is the case the following is coded.
You would code D7140 - D7210 (depending on the type of extraction) for the erupted molar along with the tooth number
D7240 - D7241 (depending on the type of extraction) for the supernumerary tooth along with the tooth number...please note depending on the carrier you would mark the tooth number as follows (if the tooth is #30) 30S for supernumerary or add 50 to the tooth nymber so if the tooth is #30 it would be marked as 80 in the tooth number area.
You will need to check with your carrier to see if they require the "S" after the tooth # or the addition of 50