OP,
No need to shape anything:
You could just fill the hole with any old off-cuts of brick or block and mortar - leave a bit of space, & when the mortar & rubble sets then bring a fresh coat of mortar level with the surrounding render - and rough up the fresh mortar to blend in as best as possible with the surrounding finished surface.
This way is cheap and as good as anything else esp. so called expensive repair kits.
When its dry paint to attempt a match.
OP,
You dont need a scratching tool - you just use your imagination and the surface of the setting sand & cement to rough-up as best you can to match the surrounding render finish. If the edges of your hole have been blended in then when the surface is dry & painted you will get the best match you are going to get.
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