All conversations you have access to are located in your inbox, where they are sorted from newest to oldest, based on the date of the last message.
In the inbox, you can filter your conversations in two ways:
Using the filters at the top of the page. These filters allow you to search for messages by company, user, or time period, and you can combine these filters.
Using the search bar above, which allows you to search using keywords. If you type multiple keywords, only conversations that include all keywords will be listed.