Mower deck How can I remove slack from deck belt

My elderly neighbor has a Craftsman lawn tractor model # 917.28856 with 24 HP engine and 42" deck. The mower deck belt seems to have too much slack in it and I have been looking at his owner's manual for a solution. the belt is installed correctly and the tension spring is installed correctly on the idler pulley.
I really don't see any instructions as to how to adjust the belt. Am I overlooking something? Any advice will be appreciated.

Thanks in advance.
Red Cox

First make sure belt is part number 429636, check belt for wear & replace if necessary. See page 18 in operators manual, v-belts, not adjustable, change after 100 hrs.

mechanic mark said:

First make sure belt is part number 429636, check belt for wear & replace if necessary. See page 18 in operators manual, v-belts, not adjustable, change after 100 hrs.

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Thanks mechanic Mark. I found that on page 18. thanks again for the help.
Red Cox