Firstly, make yarrow infused oil if you do not have some on hand already.
In a double boiler over low heat, add the yarrow infused oil and beeswax.
Stir until completely melted, about 5 minutes.
Quickly and carefully pour the mixture into metal salve tins or for boo-boo sticks, pour the mixture into lip balm tubes.
Let the salve set and cool completely before placing the lids on the tins and/or tubes.
Notes
This is a hard-set salve. I like this consistency for first aid use, as it has great staying power once applied as opposed to a softer-set salve. Having said that, if you prefer a softer salve, use 1/4 cup beeswax instead of 1/2 cup.