Option 1: Same as proposed by João Marques
On your excel sheet, include business/natural key for your foreign key.

Then modify bootstrap action logic to lookup the foreign key id using aggregate.

Option 2: Turn ON IDENTITY_INSERT on Sql Server if possible (has permissions)
Here's the documentation: https://docs.microsoft.com/en-us/sql/t-sql/statements/set-identity-insert-transact-sql?view=sql-server-ver15
Example: use Advanced SQL Node and put this code:
SET IDENTITY_INSERT [EntityName] ON;
After insertion, don't forget to turn it off:
SET IDENTITY_INSERT [EntityName] OFF;
You must bracket entity name with square bracket [ ]
Option 3 (my personal pick): Replace all auto number ID with Text data type GUID.
What is a GUID?
A GUID is an acronyom that stands for Globally Unique Identifier, they are also referred to as UUIDs or Universaly Unique Identifiers - there is no real difference between the two. Technically they are 128-bit unique reference numbers used in computing which are highly unlikely to repeat when generated despite there being no central GUID authority to ensure uniqueness.
What does a GUID look like?
A GUID follows a specific structure defined in RFC 4122 and come in a few different versions and variants. All variants follow the same structure xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx where M represents the version and the most significant bits of N represent the variant.
How unique is unique?
A GUID is a unique number that can be used as an identifier for anything in the universe, but unlike ISBN there is no central authority - the uniqueness of a GUID relies on the algorthm that was used to generate it. We'll look at the types of GUIDs later, but assuming a randomly generated GUID you have about the same chance of getting hit by a meteorite in a year as getting a collision in 10-30 trillion GUIDs.
For more info: http://guid.one/guid
You can add dependency for server action to generate guid:

Change your entity identifier data type to Text.
Use TextToIdentifier(GenerateGuid()) to generate GUID identifier.
For mobile app client action, you can use javascript to generate GUID (just google it).
If you don't understand about GUID, better pick other options.