Here are the meanings in this context:
Reach (noun) = Your potential influence on the world, or on your market. Having a big reach means many people can connect with you. Having a small reach means you cannot connect with too many people, you have a smaller influence in the world / your market."
micro-influencers = Influencers that have a smaller influence (a smaller reach).
To put you off = To make you not want to do something. To make you change your mind about doing something.
So, this sentence means, do not let the smaller influence of micro-influencers, make you not want to do this. Don't be discouraged/disappointed in micro-influencers' small reach, there must be some other advantages to them.