You can use data entities in D365 Data management to import values in tables such as sales Quotation table (SalesQuotationTable) and Quotation lines (SalesQuotationLine). Microsoft D365 FinOps already comes with data entities for each key document (Sales order, quotations etc).
Just search for data management or navigate to System Administrator>>WorkSpaces>>Data Management. There you will find among other options the tile for Data entitites.
Considering the design of the excel, it is suggested to use custom code for importing excel file into D365D&O. This will provide with a better result than data entities. Else, you will have to modify the format similar to the format provided by data entities.
However, when using custom functionality to import, you should note that you will have to write your own code to perform validations, keep track of history & handle any errors.