There is no such chemical.  The fungi responsible for the common tomato diseases (early blight, septoria leaf spot) are best dealt with using cultural methods.  These include proper watering regimens (do not water overhead or at night), careful sanitation (cleanup and don't compost debris), crop rotation (don't plant solanaceous plants - tomatoes, potatoes, peppers, etc. - in the same spot year after year), mulching to prevent splash-up during rain events, using resistant varieties, and so on.  Read here:
https://extension.umn.edu/planting-and-growing-guides/managing-plant-diseases-home-garden

There are fungicides, but they are only effective at preventing an infection from establishing on the plant, not at killing spores in the soil.  Tomatoes are susceptible to many disorders, not all fungal (e.g., viral, bacterial and abiotic).  Furthermore, fungicides must be applied before symptoms appear.  So a soil drench would never be called for.  Cultural methods are the safest and the most effective control.  Here is another reference:
https://www.vegetables.cornell.edu/pest-management/disease-factsheets/managing-tomato-diseases-successfully/