You are asking for suggestions for "fruiting" a beer. While this is typically considered a somewhat advanced process, it can easily be done with a bit of thought upfront.
Option 1 - Add fresh or frozen mango chunks in a muslin baggie into secondary for infusion. This can be expensive, and unless you have some experience, the amount of mango {fruit} to use can be tricky. Pulp can also be messy and cause you to lose beer when racking off. Frozen bags of fruit at larger stores can be your best price point.
Option 2 - Make a tincture. Pouring vodka or a neutral spirit over fruit draws out the flavors so you'll end up with a nicely flavored tincture to add to your finished beer before kegging or bottling. You can add to taste so you wont make mistakes and have a keg or batch of bottles of beer you wish had more or less flavor. I personally really like tinctures plus its not messy and full of pulp like option 1 since you'll strain the tincture thru a coffee filter or cheesecloth.
Option 3 - Flavorings/Extract. YUCKKKK.

Not really. Some of the cheaper imitation flavorings are bad and have given this option a terrible name. However, good ones exist, yet they are more of a concentrated natural flavor vs an imitation version. Silver Cloud/Apex is hugely popular natural brand and I have also used Monin which is nice. Another option is NOT to use a flavor for the entire keg at which time you are stuck with a whole keg of XXX flavored beer. Rather, I'll have several flavors like raspberry and peach too, then you can add a pump to your pint and have good varieties.
Option 4 - Make your own flavor concentrate. I use this technique to make a watermelon concentrate to add into Gose styles in the summer, but most any fruit will work like this. Juice a watermelon and collect 1/2 gallon of juice in a clean milk jug. Freeze solid, take lid off jug and let sit upside down on an open 1 quart mason jar. The flavors thaw first and drip into the jar - then stop collecting when you have a full quart. Discard the semi-clear ice block that remains in the milk jug. Freeze that quart of newly collected concentrate in a clean milk jug and again turn upside down on a pint mason jar, then collect until you have 1 pint of concentrate. This is super flavorful concentrate and 1 pint will nicely flavor a 5G batch of beer.
Hope you're not asleep by now. Enjoy