First You need to understand Websocket mechanism Refer this link (https://portswigger.net/web-security/websockets#intercepting-and-modifying-websocket-messages)
After that you have to configure Burpsuite to Intercept Websocket communication Refer this link (https://portswigger.net/burp/documentation/desktop/tools/proxy/options#intercepting-websocket-messages)
You can refer below mentioned Book for more detail understanding of Websocket Security testing. (https://www.theseus.fi/bitstream/handle/10024/113390/Harri+Kuosmanen+-+Masters+thesis+-+Security+Testing+of+WebSockets+-+Final.pdf?sequence=1)