The most important factor that affects the value of a company’s share price is their real or expected earnings. You are in a position to affect that by either causing direct loss of profit or by increasing their costs. Interfere with their efficiency, disrupt their supply chain, disturb their operations, block the flow of their system in whatever ways you can, based upon analysis.
Other factors that can affect the share price include, changes in management (which your actions will likely cause), procurement of new contracts (which your actions will likely hinder), employee layoffs or walkouts (which your actions can potentially simulate).
If you use traditional tactics of civil disobedience, sit-ins, marches, and so forth, use them to disrupt the operations of a targeted company. Shut it down. Form a picket line in the manner of striking workers to impede access to the facility, etc. This will not only potentially cause direct loss and hinder efficiency, but also the company will have to take measures to insulate itself from further actions, which will require extra costs and procedures, thus exacerbating the disruption by their own response to it.
And, of course, other tactics are conceivable.