Chart Axis Range

Generally, you select the "thing" then use the format tool on the right to make adjustments pertaining to the "thing". For a chart, select the chart, then open the format tool:

In the format tool, you can set details about the x and y axis by selecting the "Value (x)" and "Value (y)" segment controls

On Mobile it is referred to as Y Axis Scale and is under Data. I realize this likely does not apply to you but it may give you a starting point to look if nothing else.

That being said, a document that has been converted from Excel can be opened in Numbers but it is not a true Numbers document and will not always behave the same way. Nowhere is this more true, I find, than in charting. It is possible the option does not exist for a converted document. Depending on the complexity of your document you may wish to copy and paste your data into a fresh Numbers document.