You can find a development partner through networking, online research, and reviews. Here’s more detail:
Networking – ask partnering companies whether they have had experience with development companies, then research those businesses, contact representatives, and make your choice.
Search engines – go online and write a clear query with all the keywords needed for the right result. For example “Uber for trucking app development” or “developing an app for truck drivers”. Go through the first page, explore the ads, and research to find a good provider for your needs.
Reviews – Clutch, LinkedIn, Trustpilot, and other review platforms should provide you with sufficient information about app development companies from real customer messages.