This example will show you how to assign an item in a SharePoint list to someone. When that is done it will send them an email with the item information to the user AND update the item in the list to the assigned user

The Current owner column is a People picker data type and will work for my needs because the emails I will assign to are located in Office365

If you need to enter external email addresses then you may need to use a text box data type on this column

First I will Create an instant flow and select the trigger that says For a selected item

Once that is created enter the target Site Address and List name then Add an input called email

Next add an action called Get item and enter the Site Address and List Name

The Id will be the dynamic content from For a selected item

@{triggerBody()?['entity']?['ID']}

The next action I will add is a Send an email (V2) action

For the To field I will select the email dynamic content from the For a selected item

If you kept the names default you can copy past this in the field:

@{triggerBody()['email']}

Enter what you want to include in the Subject and Body

The final action will be called Update item

In my SharePoint list above I want to update the Current Owner so I will select the Email dynamic content under For a selected item in the Current owner Claims field

If you kept all the default names in my example you should be able to copy and past this code into the fields above:

Id: @{triggerBody()?['entity']?['ID']}
Title: @{outputs('Get_item')?['body/Title']}
Current owner Claims: @triggerBody()['email']

Save that flow and give the target users Run only rights to the flow

Here is how to use it

Go the the SharePoint list and select an item

In the menu click Automate and select the name of your flow

Click Continue to pass any permissions being added

The flow will then ask for an email, enter an Office365 email and click Run flow

The user will then see an email with the information I entered (I removed company sensitive data)

I can then refresh my SharePoint list and see the Current owner has automatically been updated as well

If something did not work as intended then be sure to look at the history and see any details of a failed flow