I am unsure what you mean by "infected soft pulp tissue" but I am going to assume you mean that a cavity has reached your pulp and therefore infected the nerve tissue in your molar. When this happens, your doctor will confirm with an xray as well as "endo pulp tests" to see if the nerve has really been infected and whether or not the inflammation and pain is reversible or not. If it has infected your pulp, a root canal treatment will more likely than not be recommended, taking into consideration other factors seem during this exam. Following this, usually a restoration will be placed on the tooth to restore the tooth back to structure and function, like a crown and build up. Hope this helps!
It sounds like you may possibly need to get root canal therapy on this tooth, followed by restorative treatment.
Hope that answers your question.
For any sort of possible tooth infection, the steps would include having an intral-oral exam, appropriate X-rays, dental/medical history. Depending on how severe the decay and/or infection, the doctor may recommend root canal treatment and crown, or extraction (removal of tooth), with possible pain medication and/or antibiotics. To receive a comprehensive examination and consultation, please visit your local licensed dental profession.
If you are referring to the soft tissue behind or around a tooth, then a cleaning or irrigation may be indicated. In some cases, antibiotics can be beneficial.
If you think you have an infection, call your dentist without delay.