Not sure about your model but generally you work from underneath Creda machines. Slacken off motor mount, work new belt down back ond over fly wheel then easy on to motor pully and pull motor to tension belt, hold it there and tighten mounting bolts. There may be a cover plate on base of your machine. Hope I am right but am working from memory as I did mine a long time ago.
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Try fixfault.com to fix tumble dryers.