We are truly sorry to hear about the pain and distress you're experiencing due to this mouth ulcer. We will stand with you in prayer and faith, trusting God's healing power.
Firstly, we want to encourage you with God's word. In Matthew 9:35 WEB it is written, "Jesus went about all the cities and the villages, teaching in their synagogues, and preaching the Good News of the Kingdom, and healing every disease and every sickness among the people." Jesus is still the same yesterday, today, and forever (Hebrews 13:8 WEB). He can heal you today.
Let's pray together:
"Dear Heavenly Father, we come before You in the name of Jesus Christ, seeking Your healing touch for this dear one. You said in Your word that by Jesus' stripes, we are healed (Isaiah 53:5 WEB). We claim this promise over the ulcer in the mouth. We rebuke any fear of cancer and declare that no weapon formed against this dear brother or sister shall prosper (Isaiah 54:17 WEB). We ask You to ease the pain, remove the ulcer, and restore health and strength.
We also pray for peace, that this one will not be anxious about anything, but in every situation, by prayer and petition, with thanksgiving, will present their requests to You (Philippians 4:6-7 WEB). We ask for Your comfort and encouragement while awaiting the medical procedure, and we pray that the medical professionals will have wisdom and discernment.
Lastly, Father, we pray that through this trial, this one will draw closer to You, trusting in Your goodness and faithfulness. If they have not already done so, we pray that they will call on the name of Jesus Christ, believing that He is Lord, and be saved (Acts 2:21, Romans 10:9 WEB). We thank You for Your love and faithfulness. In Jesus' name, we pray. Amen."
Regarding your fear of cancer, remember that God has not given us a spirit of fear, but of power, love, and self-control (2 Timothy 1:7 WEB). Trust in Him, and He will give you the strength to face whatever comes your way.
Lastly, we noticed that your request did not mention the name of Jesus Christ. It is only by His name that we have access to God the Father, and it is only by His name that we can be saved. As it is written in Acts 4:12 WEB, "There is salvation in none other, for neither is there any other name under heaven, that is given among men, by which we must be saved." We encourage you to put your faith in Jesus Christ if you have not already done so.