You can from the Appearance > Editor and select CSS > base.css
If the bootstrap is being added by a plugin just be mindful that updates will overwrite that change.
The code is coming from Widget Kit for Elementor. How much do you need that plugin? Looking at the base.css there is already some commented out content and looking at the code coverage is less than 5% (that is 95% of it’s not being used).
We could look at enqueing another style sheet to load after it – but it seems a bit daft to add more code if its not necessary.