The goal of a fit-gap analysis is to identify what out-the-box functionality can be used for the project. If you uncover some gaps in the out-the-box solutions to meet the project requirements, you can evaluate alternate solutions. You can start from the Dynamics 365 family of products, like Dynamics 365 Customer Insights, Dynamics 365 Business Voice, Dynamics 365 Fraud Protection, etc. Or you can search for the solutions in Microsoft AppStore.
Reference:
https://docs.microsoft.com/en-us/learn/modules/becoming-solution-architect/2-skills
https://docs.microsoft.com/en-us/learn/modules/fit-gap-analysis/5-apps
https://docs.microsoft.com/en-us/learn/modules/working-with-customer-insights/1-introduction
https://docs.microsoft.com/en-us/dynamics365/customer-voice/about