Ok, so you're asking specifically about CoinMarketcap. The answer is: You can't choose custom dates. Why? Because the CoinMarketcap site and mobile app don't offer that functionality.
What coin are you interested in historical data for? Google: [
insert coin name here] historical prices
This will likely return you a few sites that provide historical price data for the coin you have interest in, and one of these sites should allow you to customize the date range.
If that doesn't work, follow Pooya's advice below:
just calculate it on your own!
the price history is out there, you can just open up any exchange that has that coin and check the price at those two dates and then calculate the percentage change of it.
[(price2 - price 1) / price1] * 100
or
[(price2 / price1) - 1] * 100
if you are familiar with programming then you can use poloniex chart API to get the price of a specific date