When it comes to axolotls, one of the first lessons learned is to not accept advice from the pet shop about them.
You can ask the pet shop for advice on this, but they may try to sell you a bottle of bottled bacteria - this stuff is not reliable. The good bacteria you need, needs food and oxygen in order to thrive, 2 things not likely to exist in a sealed container that has been sitting on a shelf for who knows how long. Taking this shortcut now may cause your cycle to crash later - while your axolotl is in it.
If they give you proper advice, they will tell you something similar to what I have given you here and the information given on this site.
This is a paragraph from the article about Fishless Cycling under Caudate Culture that I gave you the link to: "Set up the aquarium using dechlorinated water and let it run for 24 to 48 hours. This will allow you to ascertain that all the equipment is working properly and will allow any excess dissolved gases to dissipate. Test the water for all of the above listed parameters and record the results; these will be your starting measurements. After the aquarium has been running for the recommended time period,
add a small amount of your ammonia source. (For example, use a piece of frozen brine shrimp that could cover a dime). After 24 hours, test the water and record the results. Monitor the water results every day or two. When the ammonia level begins to drop and the nitrite levels to rise, add another small piece of ammonia source to keep feeding the bacteria. Keep monitoring the water quality, and when the nitrates begin to rise again dose the tank with the ammonia source. This should be the last dose required to finish the cycle."
The ammonia source is key to starting the cycle. You can use fish food like the tropical flakes, it does not take a lot. Ammonia (from fish food, brine shrimp, fish) becomes nitrites - nitrites become nitrates - nitrates form your good bacteria that form colonies in your substrate, in your filter, just about anywhere. This bacteria keeps your environment stable (with your help) and safe for your axolotl.
Cycling is the worse part of this process, but if you are serious about this axolotl, this will need to be done in order for your tank to be safe for your new pet. Everybody out here has done this, and we can help you through it.