Change line chart point mark shapes

I've read, understood, and done my best to follow the [*CONTRIBUTING guidelines](https://github.com/jjatie/Charts/blob/master/CONTRIBUTING.md).
I am using combined charts with line chart and bar chart. I have successfully implemented the combined charts. Just have to change the line chart mark shapes from circle to oval.
I expect to change the shape of circle marks in line charts to oval marks
I tried to change the line chart renderer but had no luck. Any guidance with respect to this would be a great help!
Im using the latest version charts with Xcode 12.5 with swift 5 and macOS big Sur

Start by tracing the line chart renderer used by the combined line and bar chart in the Swift source, since the issue does not identify a file or test. Determine where circle marks are selected, change the line-chart mark shape to an oval, and verify the result in the combined chart on the stated Swift/Xcode setup.

Written by the indexing model from the issue text.