Your organization determined the significant environmental aspects and impacts.
Your organization determined priorities from improving some of those significant environmental aspects.
You can traceback all the sources that contribute to each of those significant environmental aspects to be improved. Chose the most important sources and link them to one or more processes.
So, you want to improve a significant environmental aspect, you translate that want into an environmental objective. Now, you can relate that environmental objective to one or more relevant processes.
For example, yesterday I audited an organization that wanted to improve the unitary consumption of energy. As an opportunity for improvement I wrote in the report that they can identify the great sources of energy consumption and act on those locations, on those processes.