Best option is
05646 from Guwahati (GHY) to Danapur (DNR). It departs from GHY on Sundays and Wednesday at 16.55 and arrives Danapur on next day i.e Mondays and Thursdays at 13.50
From Danapur take 02296 Sanghamitra Express to Bengaluru it departs at 20.10 so you will have roughly about 6hrs of layover at Danapur. I feel this is best option to reach Bengaluru from Guwahati at this time