Could you please share more details about your scenario?
Could you please show a bit more about the SharePoint integration within your Dynamics 365 environment?
Further, Do you want to update a account when a file is uploaded in your SharePoint?
For your first question, if you want to fire your flow when a file is uploaded in your SharePoint (library), I think the "When a file is created (properties only)" trigger or the "When a file is created in a folder" trigger (all SharePoint triggers related to files could achieve your needs) could achieve your needs. More details about the SharePoint triggers related to files, please check the following article:
For your second question, if you want to update an account in Dynamics 365 within Microsoft Flow, you should find the specific account firstly. You could use the "List records" action of Dynamics 365 connector to find the specific account based on some filter conditions wihtin your flow. Then use the "Update a record" action to update the account record. I have made a test on my side and please refer to following flow's configuration:
Within Record identifier field of "Update a record" action, type the following formula:
Please check and see if the following article would help in your scenario: