Conservation assessment on biodiversity - HELP needed

I'm a university student currently undertaking a project whereby I need to analyze terrestrial vegetation of a particular location. I am finding a difficulty using biodiversity indices, including Shannon Diversity Index, Simpson's Dominance Index, and Simpson's Diversity Index. These require that during sampling one calculates the abundance of species. However instead of abundance I used percantage coverage. Does anyone know how I can replace the latter by the former in these equations?

I hope this is the right place to ask such questions.