Safest option would be to do it with a therapist with experience in ERP. If its severe OCD please get therapy from a therpist who has ERP Experience
However, here are some self help books you may try:
1.The OCD workbook- Bruce M Hyman, Cherry Pedrick
2. Getting over OCD a 10 step workbook - Jonathan Abramowitz
3. Breaking free from OCD - Fiona Challacombe, Victoria Bream Oldfield, Paul Salkovskis
Next Steps
contact a Clinical psychologist or Psychiatrist with experience in ERP
Health Tips
ERP is tough work, better to work both with help of self help as well as in therapy.