If you're talking about the cape, you can get it in bedrock edition (not java) by completing every challenge in the official mcc event server. Mojang and MCC partnered, so you can get an actual cape. The list of challenges is automatically in the 7th slot of your hot bar. To join the server, simply "Join the Event". Btw #2, rumour has it that the cape will come to java in a few weeks, but it hasn't been confirmed, to my knowledge, that is.
If you're talking about the skin, then you can enter their username into namemc.com, click the skin you want to use, then press download. If you don't know their name, then ig just search for them/their name/their skin.
