It's mucus retention cyst or mucocele...often happened secondary to trauma.
It's soft , small lump filled with mucus . It forms when minor salivary gland duct or gland get blocked or damaged.
Next Steps
most of observe because sometimes it will resolve by itself.
take dental opinion also
but i will suggest in your situation if no change even after few weeks of observation and it's still persisted or its increase in size, can plan for surgical excision or laser ablation.
recurrence chances are common in this.
malignant chances are rare but it's always better to rule out by excision.