Tooltip Dataset labels missing

Just to follow up on this, I can fix the tooltip labels in the browser console using the code below:

m_chart_chartjs_3889_1.chart_args.options.plugins.tooltip.callbacks.label = function(context) {
                        var label = context.dataset.label || '';
                        if (label) {
                            label += ': ';
                        }
                        if (context.parsed.y !== null) {
                            label += context.parsed.y;
                        }
                        return label;
                    }

But how do I modify “m_chart_chartjs_3889_1” before it has been created? For more context, I can add a sum at the bottom of the tooltip using the chart defaults:

Chart.defaults.plugins.tooltip.callbacks.afterBody = (ttItem) => (Sum: ${ttItem.reduce((acc, val) => (acc + val.raw), 0)});

But when I try to modify the default label function, it reverts to a different function after the chart loads. This is what I want it to be:

Chart.defaults.plugins.tooltip.callbacks.label = function(context) {
                        var label = context.dataset.label || '';
                        if (label) {
                            label += ': ';
                        }
                        if (context.parsed.y !== null) {
                            label += context.parsed.y;
                        }
                        return label;
                    }

This is what it loads as when I access it via the console:

>m_chart_chartjs_3889_1.chart_args.options.plugins.tooltip.callbacks.label
< a=>m_chart_chartjs_helpers.chart_tooltip_label(a,r,t,e,_)

I think it is getting overwritten at some point. Any help would be greatly appreciated!