It is not very clear what you wish to achieve 

You can use 'query list' querying [Numbers] column on entire list upto 5000 items or based on a filter or number

You can use for each to get value of each [Numbers] column

Then use do calculation to subtract 1 from the number and capture in a variable 

Finally use update item action to replace the value of [Numbers] value with caculated value

Steps I suggested will work

1) Query list for all list items - single output - capture results in a collection variable 'varNumCol'

2) Use for each loop for 'varNumCol' and capture result in a integer variable 'varNumber'

3) use 'do calculation' inside 'for each loop' -  'varNuber - 1' capture in another number variable 'varNewNumber' 

4) Update list item where 'Current Item Number' = 'varNumber',  update '[Numebr]' field to 'varNewNumber'

5) Create a site workflow as a site workflow to start this workflow and add a schedule if you need periodic runs

Hope this makes sense, let me know if you need further help