Welcome to the forum Mike. Hardware stores often stock quick links & half links which aid in either lengthening or shortening chains. You will need to know what size chain you have to buy chain or the proper chain links. There are several chain sizes used on moto-bikes (motor drive chain) half inch, 415 or 415 H chain is a common size for kit motors, and pedal side chain comes in different sizes as well. If you have a shifter setup on your bike that uses only one chain to drive both pedal & motor to the rear wheel that's another consideration.
Tell us what you have i.e. 2 stroke motor kit or if you're referring to the pedal chain. Photo of bike usually helps. Without your input we're stuck with guessing what your need is.
When you're dealing with chains you need to have a chain break tool if you plan on staying with this hobby and how to use it when working with chain. YouTube videos are often your best friend when working on any bike including the motorized ones. Not all videos are good but even those are better than guessing!