Install MathWallet https://mathwallet.org
Switch Network to 'Moonriver'
Import the 0x formatted receiver wallet when you participate Moonriver crowdloan
Click the 'DApp Store' button, and open the 'Moonriver Apps'
Or open the link: https://apps.moonbeam.network/moonriver
The app will connect to Moonriver wallet automatically
Then you can click the 'Claim' button to withdraw MOVR to your Moonriver wallet
Click 'Accept' on the popup window to confirm the claim operation.
Then you can install the MathWallet app to start using more DeFi apps on Moonriver.