Step 2: when you change the amount of credit allocated to a channel, you're increasing or decreasing the % of conversions that this channel will make up.
For example, if you type 1.1 in the Credit Redistribution tool for Paid Search, you will increase its share of conversions by 10%. \
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Similarly if you want to decrease the conversion share of a given channel by 10%, type 0.9 in the tool custom credit box.